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2025/05/22
An inductor is one of the fundamental passive components in electronic circuits, alongside resistors and capacitors, collectively known as the three basic passive elements. The core working principle of inductors is based on Faraday's law of electromagnetic induction: when current flows through a conductor, it generates a magnetic field around it; conversely, when the magnetic field around a conductor changes, an electromotive force is induced in the conductor .
Inductors are typically constructed by winding wire around a magnetic core material. When current passes through the coil, it produces magnetic flux within the coil. According to Lenz's law, inductors resist changes in current. Specifically: when circuit current increases, the inductor generates an induced electromotive force in the opposite direction to the power source to resist the current increase; when circuit current decreases, the inductor generates an induced electromotive force in the same direction as the power source to resist the current decrease .
This characteristic allows inductors to store energy in their magnetic field and release this energy when needed. This energy storage and release property forms the foundation for inductors' key roles in electronic circuits .
The basic unit of inductance is the Henry (H), symbolized as H, which is a derived unit in the International System of Units (SI). One Henry is defined as: when current through a conductor changes at a rate of one ampere per second, it produces an electromotive force of one volt across the conductor. In practical applications, since one Henry is relatively large, commonly used units include :
The main methods for measuring inductance include :
LCR Bridge Method: Using an LCR meter to measure inductance based on the bridge balance principle, which is the most common precise measurement method.
Resonance Method: Forming an LC resonant circuit with the inductor under test and a known capacitor, then calculating the inductance value by measuring the resonant frequency. The formula is: L = 1/(4π²f²C), where f is the resonant frequency and C is the known capacitance value.
Impedance Analyzer Method: Using an impedance analyzer to measure the impedance characteristics of the inductor at different frequencies, thereby deriving the inductance value and its frequency characteristics.
Self-induced EMF Method: Based on the basic definition of inductance, calculating the inductance value by measuring the induced electromotive force produced during current changes.
In actual measurements, factors such as test frequency, test current magnitude, and ambient temperature must be considered for their effects on measurement results. High-precision measurements typically need to be conducted under specific standard conditions .
Inductors serve multiple important functions in electronic circuits, with their basic roles primarily manifested in the following aspects :
Inductors can store electrical energy in the form of a magnetic field and release it when needed. This characteristic makes them play a crucial role in switch-mode power supplies, DC-DC converters, and other circuits, enabling efficient energy transfer and conversion .
Inductors have impedance characteristics to AC signals, with impedance increasing with frequency (XL = 2πfL). This allows inductors to effectively block high-frequency signals while allowing DC or low-frequency signals to pass through, making them widely used in power supply filtering and signal filtering circuits .
Inductors combined with capacitors can form LC resonant circuits that produce oscillations at specific frequencies. This characteristic is crucial in RF circuits, oscillators, and tuning circuits, forming the foundation of wireless communication systems .
In high-frequency circuits, inductors are commonly used in impedance matching networks to ensure maximum power transfer of signals and reduce reflection losses .
Specially designed inductors (such as common-mode inductors) can effectively suppress electromagnetic interference in circuits, improving the electromagnetic compatibility (EMC) performance of systems .
Inductors are widely applied in modern electronic technology, with major application fields including :
Choosing appropriate inductors is crucial for circuit performance. Below are the basic considerations for inductor selection :
Calculate the required inductance value based on circuit requirements, considering the tolerance range of inductance values (typically ±5%, ±10%, ±20%). In switch-mode power supply applications, the inductance value directly affects ripple current magnitude and operating mode (Continuous Conduction Mode CCM or Discontinuous Conduction Mode DCM) .
When selecting inductors, ensure that the operating current is below the rated current and the peak current is below the saturation current .
The DC resistance of an inductor directly affects power loss and efficiency. In high-current applications, inductors with low DCR values should be selected to reduce heat generation and improve efficiency .
The self-resonant frequency of the inductor should be much higher than the circuit operating frequency to ensure the inductor maintains good inductive characteristics within the operating frequency range .
Select inductors of appropriate size according to PCB space limitations. Common packages include SMD (0402, 0603, 0805, 1210, etc.) and THT (through-hole) .
For EMI-sensitive applications, consider using shielded inductors to reduce magnetic field leakage interference with surrounding circuits .
Consider the performance variations of inductors within the operating temperature range, especially for applications working in extreme temperature environments .
While meeting technical requirements, comprehensively consider cost factors to select inductors with the best cost-performance ratio .
As a fundamental electronic component, inductors play an irreplaceable role in modern electronic systems. A deep understanding of inductor working principles, characteristic parameters, and application fields is crucial for electronic engineers designing high-performance, high-reliability electronic systems. With the continuous development of electronic technology, inductors are also continuously innovating in materials, structures, and manufacturing processes, enabling possibilities for wider applications .
In the circuit design process, rational selection and application of inductors can not only achieve the expected circuit functions but also improve system energy efficiency, reliability, and electromagnetic compatibility, providing strong support for overall product performance enhancement .
